Method of determining the permeability of earth formations



lwwaan Fxpanii METHOD OF DETERMINING THE PERMEABILITY OF EARTH FORMATIONS R J D R A H N H E L J P Filed Dec. 15, 1941 CONDUCT/WT) B/F/DGE IIYJULA T/IVG NENEEA 34 RES/SMNCE WIRE GECT/FODE .36 6 MEASURING INVENTOR. P/u/7'o 1/ Lahn/varc/ Jr.

W E $1M Patented May 29, 1945 METHOD OF DETERMINING THE HERME- ABILITY OF EARTH FORMATIONS Philip J. Lehnhard, J12, Houston, Tex., assignmto The Dow Chemical Company,

Midland,

Mich, a corporation of.Mlchigan Application December 15, 941, Serial No. 422,967

2 Claims.

The invention relates to a method of determining the permeability of formations or portrons thereof penetrated by the bore of a well.

1 It is more particularly concerned with a method wherein rates of flow of fluids from the Well bore into known portions of the formations surrounding the well bore are employed to indicate the permeability of the surrounding formations.

In introducing liquid agents into an earth or rock formation such as, for example, when introducing acid solutions into a porous, calcareous productive formation penetrated by the bore of an oil well, it is desirable to know which portion of the formation is more permeable so that the fluid treating agent may be controlled. permitting its injection into the least permeable sections in order that a more desirable result may be obtained as regards the increased production. In many instances such as, for example, cementing operations, well completions, and formation testing, it is similarly desirable to obtain knowledge readily relative to the permeability of the various strata or sections thereof penetrated by the bore of a well.

It is, therefore. the principal object of the invention to provide a method whereby the permeability to fluids of several strata, or selected sections of one stratum, may be readily determined.

Another object of the invention is to provide a method whereby the relative permeability of the vawell bore can be readily ascertained so as to mow a chmplete'jperm'ealfility pro e m" th us permeable sections penetrated bv the well bore.

Other further objects and advantages of the invention will be apparent during the course of the following description.

The invention, then, consists in the method hereinafter more fully described and particularly pointed out in the claims, the accompanying drawing, and the following description setting forth in detail a mode of carrying out the invention, such mode illustrating, however, but one of the various ways of putti'ng the invention into effect.

Figure 1 is a digrammatic view partly in section of an oil. well equipped for carrying out a permeability determination according to the method of theinvention.

Figure 2 is a detailed view in cross section of the lower portion of the apparatus adapted to be used in connection with the permeability determination.

well bore is cased with metal pipe 2 while the lower portion 3 of the well bore penetrates a permeable stratum 4, an impermeable stratum 5, and a permeable stratum 8. The well tubing string 1 acts to carry or support a measuring device 8 adapted to indicate the level of a conducting fluid in the well bore. This device is shown located adjacent the productive stratum 6 so that the level of the fluid may be ascertained and held at a point near the top of stratum 6. The lower portion 3 of the well bore, together with the well tubing, is shown filled with an electrolyte so1ution 9, such as brine, up to a point l0 adjacent the upper level of the permeable stratum 6. The remainder of the well bore'consisting of the ,an-

nular space between the tubing and the casing is shown filled with a nonconductive fluid ll such as oil. Above the ground level pipe l2 controlled upper end of the tubing string I an electrical conducting cable [8 passes over sheave 9 to carrying reel 20. The conducting cable l8 contains two separate conductors and serves to carry current'to and from the measuring device carried by the lower end of the tubing and also serves asfa means whereby the measuring device may be raised and. lowered through the tubing string.

An electric circuit is employed in connection with l the measuring device 8 for the purpose of indieating the level of the electrolyte and may 1:

shown, consist of a source'ofalternating current,

such as a 25 or cycle volt alternating cur-- rent source, the terminals of which are connected nected to the-reel shaft and reel shaft support.

22 which in turn is electrically connected with one conductor of conducting cable l8. The other lead from the conductivity bridge is connected As shown in Figure 1 the upper portion l of the 55 to a ring 23 insulated from reel 20 by insulation 24. The ring 23 is connected to theotherlead of conducting cable l8. A brush 25 is provided1to maintain electrical contact between the bridge lead and the ring 23 as the reel is rotated.

In the more detailed view of the measuring (is-- vice shown in Figure 2 a conventional iron collar or coupling 26 is threaded to the lower end of the tubing string 1 and a tapered seat member 21. Attached to the seat member 21 in screw thlreaded engagement therewith is a packing gland 28 through which the tubular body member 29 can be slidably moved in sealing-relationship. The tubular body member 29 of the measuring device formed of metal or other electrically conducting material is shown enlarged at the upper end to form a tapered seating portion 30 which conforms to the inner surface of the seat member 21, thus producing a seal when the surfaces are maintained in. contacting relationship. Entry ports 3! and exit orts 32 are provided at the upper and lower ends, respectively, of the tubular member 29 and serve as a means whereby liquid can pass through the measuring device 8 into the well bore from the well tubing 1. The'section of the tubular member 29 carries an electrically insulating shell 33 made of Bakelite, hard rubher, or the like. Completely embedded in the insulating shell is a resistance wire 34 which is wound spirally about the insulating shell 33. The resistance wire is connected at its upper end to an electrode 35 and at its lower end to an electrode' 36 mounted on the insulating shell. The outer conductor 31 of the conducting cable l8 -mayconsist of woven wire and is connected to ,the upper end of tubular element ,29 as by clampr ting means 38 and may be further secured thereto as by soldering, brazing, or the like. The inner conductor 39 of conducting cable i8 is in- =sulated from the outer conductor 31 by insula- .tion 40. Theinner conductor 39 passes through ,the tubular element 29 and is connected to the ,,upper electrode 35 mounted on shell 33 through insulating bushing 4|, while the electrode is also connected to the upper end of resistance wire 34.

In carrying out the method of the invention wherein it is desired to ascertain the relative pertime a nonelectrolyte is introduced into the casing through pipe l2 while valve I3 is maintained open- When the electrolyte reaches the bottom of the well and rises in the well bore to a point Qadjacent the top of the stratum 6, the lower elec- Qigrode on the measuring device will be contacted and the electric circuit will be completed through ithe conducting cable l8 and tubular element 29, f which will be indicated on the conductivity bridge ,21. Thereafter pressure is applied so as to force ""Llectrolyte'into the formation and the pumping 'rates of the electrolyte into the tubing and the ,Jronelectrolyte into the casing are controlled so "that the level of the electrolyte is maintained at the desired point between the two electrodes in 'the well bore. If at any time the electrolyte reaches the upper electrode a marked increase in ,current flow will be noted and indicated by the unbalancing 'of the galvanometer in the conductivity bridge. Thus, it will be readily possible to .keep the level of the electrolyte at a point heitween the two electrodes or closely adjacent the upper level of stratum 6. From a knowledge of the pressures being applied and the rate at which the electrolyte solution is entering stratum 6 it will be possible to ascertain the relative permeability of stratum 6. It is preferable to maintain the rate of flow of fluid and the pressure being appled at a nearly constant or fixed figure during the determination of the permeability of a specific section so that the permeability figure will be more readily ascertainable. If it is then further desired to determine the permeability of upper stratum 4, the measuring device will be relocated so that the electrodes become positioned adjacent the upper level of stratum 4, the rate of introduction of the electrolyte being increased so as to allow its level to reach the upper level of stratum 4. Thereafter the introduction of fluids through the tubing and easing will be controlled so as to maintain the level adjacent the upper level of stratum 4, whereby the volume of fluid entering each strata will be known. From a knowledge of the amount entering the lower stratum at a given pressure, it.will be readily appreciated that the additional amount of fluid being pumped at a known pressure has entered stratum 4. From a knowledge of the pressure being applied and the volumes of fluid being injected into each stratum it willbe possible to accurately calculate the relative permeability of the upper stratum.

In a similar manner, if it is desired to ascertain'the permeability of a specific section of a single roductive stratum, it will only be neces- ,sar v to first. ascertain the permeability of the formation up to the lower level of the specific section and thereafter control the level of the fluid about the upper levelof the stratum while applying sufficient pressure to force fluid into the formation. Additionally, 'it will be understood that in the same manner the permeability of all sections of a formation of considerable extent may be readily determined. In the foregoing manner it is possible to readily obtain a complete permeability profile of the entire open bore hole.

While it is generally preferred to carry out the method employing the apparatus described herein it is to be understood that other types of apvparatus may be employed forcarrying out the method. I

I claim:

1. In a method of determining the permeability of a formation penetrated by the bore of a well, the steps which comprise introducing two immiscible fluids intothe well bore, one being of higher specific gravity and electrical conductivity than the other, so as to form two layers of fluid in the well bore, ascertaining the position of one of the fluids in the well bore, maintaining one of said fluids adjacent the portion of the formation the permeability of which is to be tested, by controlling the rate of introduction of said fluids into the well bore and forcing the fluid adjacent the section of the formation to be tested into that portion of the formation at a known rate and under a known pressure, whereby said known rate gives an indication of the permeability of that portion of the formation.

2. In a method of determining the permeability of at least a portion of the formation penetrated by the bore of a well, the steps which comprise introducing oil and brine into the well bore while maintaining said fluids out of contact with each other until they reach the lower portion of the well bore, electrically ascertaining the liquid interface in the well bore, controlling said interface at a point adjacent the upper level of the formation to betested, applying pressure so as to force the brine into said formation at a known rate under v the known pressure, whereby said known rate gives an indication of the permeability of that section of the formation."

PHILIP J. LEHNHARD, JR. 

